Electron tube



is in;

Oct. 25, 1960 T. D. PETERSON 2,957,996

ELECTRON TUBE Original Filed Ju1y l6, 1957 IN VE N TOR THOMAS D. PE TERSOA/ Unitfid States ELECTRON TUBE 15 Claims. (Cl. 313-456) This invention relates to electron discharge devices and to improvements in electrode cages for use in electron tubes, particularly magnetron beam switching tubes. This application is a continuation of application Serial No. 672,156 filed July 16, 1957, now abandoned.

. Generally, an electrode cage comprises a plurality of elongated electrodes arranged in a predetermined physical relationship and secured together at their opposite ends by means of insulating disks or plates. The electrode dimensions and spacings in an electrode cage must be very accurate to achieve the required electron tube uniformity and efiiciency of operation. To achieve such accuracy, the insulating disks in electrode cages are generally. as smooth and uniform as possible, and the most suitable material for making smooth uniform spacers is mica. However, smooth mica spacers in electrode cages may become electrically charged dueto electron bombardment, and, in addition, metallic particles may sublime from other electrodes in the cage and may deposit on the micaspacers and form troublesome electrical leakage paths.

. These problems are particularly critical in magnetron beam switching tubes of the type which operate with crossed electric and magnetic fields and which are described in U.S. Patent No. 2,721,955 to Sin-Pih Fan et al. Up to the present time, a completely satisfactory solution to the foregoing problems has not been achieved, particularly as they affect magnetron beam switching tubes, and a satisfactory manufacturing process for tubes of this type has been comparatively expensive and timeconsuming.

Accordingly, an object of the present invention is to provide :an improved electrode cage for use in electron tubes.

Another object of the invention is to provide an improved electrode cagev for use in a magnetron beam switching tube.

Another object of theinvention is to provide an improved magnetron beam switching tube characterized by stability and uniformity in operation.

A. further object of the invention is to provide an improved magnetron beam switching tube characterized: by its economy of manufacture.

In brief, an electrode. cage embodying the invention and. adapted. for use in an electron tube and particularly a magnetron beam switching tube includes a central elongated cathode electrode surrounded by groups of electrodes which are adaptedto form and receive an electron beam from the cathode. The various electrodes are secured together in the cage by means of insulating end disks secured to. the opposite ends of theelectrodes. The insulating disks, which are preferably of mica, are pro.- vided with a roughsurface coating which. comprises, essentially, a finepowdered glass frit which includes a magnetic material. The rough surface of, the coating substantially prevents the formation of electricalleakagepaths, andthe magnetic characteristic imparted to the coating atent Patented on. 25, 1.960

improves the orientation of the magnetic field in the tube and the resultant operation of the tube.

The invention is described in greater detail by reference to the drawing, wherein the single figure is a perspective view of a magnetron beam switching tube embodying the invention.

The principles of the invention are applicable to electron tubes in general but are described herein as they apply to a magnetron beam switching tube of the type shown and described in the above-identified U. S. patent. Re-- ferring to the drawing, a magnetron beam switching tube: 10 includes a glass envelope 12 having a base 14 through which pins 16 extend. The tube 10 contains an electrode cage 17 which comprises a central axially positioned longitudinal electron-emitting cathode 18 surrounded by several coaxial arrays of electrodes. On a circular locus nearest to the cathode are longitudinally elongated beam forming and holding electrodes 20, called spade electrodes. Beyond the spade electrodes on another circular locus are similar longitudinally elongated output or target electrodes 22 positioned so as to cover the spaces between spades and to collect beam current flowing into these spaces Between one edge of each spade and the near edge of the target electrode is positioned a longitudinal rod-like switching grid electrode 24-. An openended cylindrical permanent magnet 26 surrounds the tube 20 and is coaxial therewith.

The electrodes of the cage 17 are secured together by means of top and bottommica disks 28 and 30 respectively which have inner facing surfaces 32 and 34 that are accessible to electrons flowing from the cathode to the other electrodes. The mica disks are provided with suitable apertures to receive and secure end portions of the electrodes, as is well known in the art.

According to the invention, the mica disks 28 and 30 and preferably their facing inner surfaces 32 and 34 are treated so that they will not become electrically charged during the operation of the tube and so that sublimed metal will not be deposited thereon in continuous electrical leakage paths. This treatment comprises the provision of a rough glass coating 36 on the surfaces of the mica. The material employed for the glass coating on the mica disks comprises, essentially, a fine powdered glass frit suspended in a suitable removable carrier. The glass may be of substantially any type. One suitable commercially available material for the coating includes powdered. lead borosilicate glass and a black pigment carried in isopropyl alcohol. The glass is a type which flows at about 950 F., and the pigment comprises a mixture of oxides of cobalt, chromium, and iron, which are magnetic and impart magnetic properties to the coating. This glass frit may be obtained from B. F. Drakenfeld & Co., Inc. as type 2342 glass frit. Another suitable coating material includes powdered lead bisilicate glass in an aqueous carrier. This glass flows at about l.400 F. This material may be obtained from Dupont as. type 8291 glass frit. A pigment or coloring may or may not be included in the glass frit coating 36 so long as the magnetic properties are present.

In. preparing the mica disks 2% and 3 for use in the cage 17, the selected powdered glass coating mixture is sprayed, painted, or otherwise applied to the surface or surfaces to be treated. The coating is then sintered to cause it to adhere to the mica disks. The sintering may be accomplished by baking at a temperature high enough to achieve the desired adherence without adversely affecting the mica. Baking. at about 900 C, for about ten minutes is satisfactory.

In assembling the tube 10, the electrode cage 17 is mounted in the tube envelope 12 in conventional fashion, and then the tube isbaked out, evacuated, and sealed according to standard vacuum tube techniques. Gene1'-' ally, tubes of this type are aged, for example, by the application of a comparatively high voltage between cathode and spades for a comparatively long time. However tubes embodying the invention have favorable operating characteristics even without aging. For example, tubes utilizing the invention have an operating range of about 70 to 150 volts (spade-to-cathode voltage) without aging, while similar tubes with untreated mica plates have had operating ranges of about 80 to 120 volts after about 72 hours of aging. In addition to having a wider operating voltage range with reduced aging, tubes embodying the invention have greater operating stability, improved magnetron cutoff and more uniform operating characteristics at each electron beam-receiving position.

What is claimed is:

1. An electrode cage for use in an electron tube, said electrode cage including an electron-emitting cathode and an output electrode, means in operative relation with said electrodes providing a generally longitudinal magnetic field lying substantially transverse to the path of current flow between said cathode and said output electrode, disks of insulating material supporting and securing said cathode and said output electrode to form said cage, said disks having rough surfaces including magnetic material in a glass carrier medium, said disks lying transverse to said longitudinal magnetic field so that the lines of flux of said magnetic field are intercepted by said disks.

2. An electrode cage for use in an electron tube, said electrode cage including an electron-emitting cathode and an output electrode, means in operative relation with said electrodes providing a generally longitudinal magnetic field lying substantially transverse to the path of current flow between said cathode and said output electrode, disks of insulating material supporting and securing said cathode and said output electrode to form said cage, and a coating of powdered glass including magnetic material on each of said insulating disks, said disks lying transverse to said longitudinal magnetic field.

3. An electrode cage for use in an electron tube, said electrode cage including an electron-emitting cathode and an output electrode, means in operative relation with said electrodes providing a generally longitudinal magnetic field lying substantially transverse to the path of current flow between said cathode and said output electrode, mica disks supporting and securing said cathode and said output electrode to form said cage, and a coating of powdered glass including magnetic material on each of said mica disks, said disks lying transverse to said longitudinal magnetic field.

4. The cage defined in claim 3 wherein said coating includes powdered glass selected from the group consisting of lead borosilicate glass and lead bisilicate glass.

5. A magnetron beam switching tube including an envelope, and an electrode cage mounted within said envelope, said electrode cage including a central cathode electrode, a plurality of groups of electrodes surrounding said cathode and adapted to receive an electron beam from said cathode, means in operative relation with said electrodes providing a generally longitudinal magnetic field lying substantially transverse to the path of current flow between said cathode and said groups of electrodes, disks of insulating material supporting all of said electrodes and securing them together to form said cage, said disks having rough surfaces including magnetic material, said disks lying transverse to said longitudinal magnetic field.

6. A magnetron beam switching tube including an envelope, and an electrode cage mounted within said envelope, said electrode cage including a central longitudinal cathode electrode, a plurality of groups of electrodes surrounding said cathode and adapted to receive an electron beam from said cathode, means in operative relation with said electrodes providing a generally longitudinal magnetic field lying substantially transverse to the path of current flow between said cathode and said groups of electrodes,

disks of insulating material supporting all of said electrodes and securing them together to form said cage, each of said disks having a rough surface coating of an insulating material including magnetic material, said disks lying transverse to said longitudinal magnetic field.

7. A magnetron beam switching tube including an envelope, and an electrode cage mounted within said envelope, said electrode cage including a central longitudinal cathode electrode, a plurality of groups of elongated electrodes surrounding said cathode and adapted to receive an electron beam from said cathode, means in operative relation with said electrodes providing a generally longitudinal magnetic field lying substantially transverse to the path of current flow between said cathode and said groups of electrodes, disks of insulating material positioned at the ends of said electrodes and supporting all of said electrodes and securing them together to form said cage, said disks having a rough surface coating of an insulating material including magnetic material, said disks lying transverse to said longitudinal magnetic field.

8. A magnetron beam switching tube including an envelope, and an electrode cage mounted within said envelope, said electrode cage including a central longitudinal cathode electrode, a plurality of groups of elongated electrodes surrounding said cathode and adapted to receive an electron beam from said cathode, means in operative relation with said electrodes providing a generally longitudinal magnetic field lying substantially transverse to the path of current flow between said cathode and said groups of electrodes, disks of insulating material spaced apart at opposite ends of said electrodes and supporting all of said electrodes and securing them together to form said cage, said disks having a rough surface coating of an insulating material and a magnetic material, said disks lying transverse to said longitudinal magnetic field.

9. The tube defined in claim 8 wherein said coating includes a powdered glass material.

10. A magnetron beam switching tube including an envelope, and an electrode cage mounted within said envelope, said electrode cage including a central longitudinal cathode electrode, a plurality of groups of elongated elec-v trodes surrounding and generally parallel to said cathode and adapted to receive an electron beam from said cathode, means in operative relation with said electrodes pro viding a generally longitudinal magnetic field lying substantially transverse to the path of current flow between said cathode and said groups of electrodes, a mica disk secured to said electrodes at opposite ends thereof, said mica disks having facing surfaces, and a rough coating including a magnetic material on said facing surfaces, said disks lying transverse to said longitudinal magnetic field.

11. The tube defined in claim 10 wherein said coating comprises a glass selected from the group consisting of lead borosilicate glass and lead bisilicate glass.

12. The tube defined in claim 10 and including a cylindrical magnet surrounding said electrodes.

13. An electrode cage for use in an electron tube, said electrode cage including an electron-emitting cathode and an output electrode, means in operative relation with said electrodes providing a generally longitudinal magnetic field lying substantially transverse to the path of current flow between said cathode and said output electrode, disks of insulating material supporting and securing said cathode and said output electrode to form said cage, said disks having surface coatings of a material including a magnetic substance in a glass carrier medium, said disks lying transverse to the longitudinal magnetic field.

14. A magnetron beam switching tube including an envelope, and an electrode cage mounted within said envelope, said electrode cage including a central cathode electrode, a plurality of groups of electrodes surrounding said cathode and adapted to receive an electron beam from said cathode, means in operative relation with said electrodes providing a generally longitudinal magnetic field lying substantially transverse to the path of current flow between said cathode and said groups of electrodes, disks of insulating material supporting all of said electrodes and securing them together to form said cage, said disks having surface coatings of a material including a magnetic substance, said disks lying transverse to said longitudinal magnetic field.

15. The tube defined in claim 14 wherein said coatings are dark in color to promote heat radiation.

References Cited in the file of this patent UNITED STATES PATENTS Krahl Sept. 15, Cardell Jan. 11, Clifiord Apr. 15, Fan et al. Oct. 25, Klopping Aug. 21, Pritikin et a1. Dec. 31, 

